The present invention relates generally to napped fabrics and methods of producing same and, more particularly, to a warp-knitted fabric capable of being napped on both its technical face and technical back surfaces and a method of producing such fabric on a warp-knitting machine equipped with a pile loop forming device.
Napping is a conventional technique for producing a plush surface effect on textile fabrics by brushing the fabric surface, typically with rotating napping cylinders equipped with wire card clothing or another suitable brushing surface. Napping may be carried out as a finishing technique on many varying forms of woven and knitted textile fabrics, but normally it is considered necessary that the fabric have a suitable pile or other raised nappable surface extending from the woven or knitted fabric substructure so that napping can be accomplished without damaging or weakening the structural integrity of the fabric.
In warp-knitting technology, fabrics of a multi-bar construction having facing warp yarns interknitted into a ground yarn substrate to present extended floats, or "underlap" loops, of the facing yarn on the technical back of the fabric have conventionally been considered well adapted for napping on the technical back in that the float or underlap structure may be readily worked by napping cylinders without engaging the fabric substrate. However, at the opposite technical face of the fabric, the facing and substrate yarns are knitted in plated relationship which produces a desirably smooth technical face. As a result, it is normally undesirable to attempt to nap the technical face of the fabric since the facing and substrate yarns are not sufficiently distinct to avoid potential damage to the substrate, although some commercial fabrics of this type have been produced with a fully nappd technical back and a lightly napped technical face to provide a dual-faced napped surface effect to the fabric, e.g., a fabric designated as "FLANNEL FLANNEL II" produced by the assignee of the present invention.
It is also known in warp knitting technology to knit multi-bar fabrics with a terry loop surface effect by "overfeeding" a facing yarn at a greater rate than the substrate ground yarns whereby the excess facing yarn is forced outwardly from the fabric substrate in the form of elongated terry-like loops appearing at the technical face of the fabric and, in the case of most two-bar fabrics, also at the technical back of the fabric. However, as is well known, the degree of yarn overfeeding is relatively restricted under conventional warp knitting technology by the need to maintain minimal levels of tension in the overfed yarn. Further, as a result, certain relatively strong filament yarns, e.g. polyester and nylon yarns, tend to resist overfeeding and cannot normally be knitted in this manner. At the same time, the relative degree of overfeeding of the facing yarn in relation to the ground yarn is further restricted if an extended underlap construction is utilized. Accordingly, terry-type warp knitted fabric produced by this overfeeding technique is conventionally considered unsuitable for napping on both the technical face and back of the fabric.
U.S. Pat. No. 4,567,075, to Krawczyk, discloses a specially designed warp knitted blanket fabric of a minimum three-bar construction which is capable of being napped on both the technical face and back of the fabric. Basically, the fabric includes three sets of warp yarns, a set of ground yarns forming a fabric substrate to provide longitudinal stability to the fabric, a first set of facing yarns overfed to form nappable terry-type loops on the technical face of the fabric, and a second set of facing yarns formed in relatively extended nappable floats or underlap loops on the technical back of the fabric while also providing lateral stability thereto. While this fabric solves the deficiency of the above-discussed fabrics in being nappable on only one surface, the requirement of three sets of warp yarns makes the fabric relatively thick so as to be generally unsuitable for most apparel or like uses other than as a blanket fabric as disclosed and, furthermore, requires considerably greater amounts of yarn thereby increasing the overall cost of the fabric.
In recent years, pile loop forming devices have come into widespread use as an attachment to warp knitting machines to permit the formation of underlap loops of an extended terry-like pile-type character. Essentially, these devices utilize a set of sinker members mounted to one yarn guide bar of a conventional multi-bar warp knitting machine to enable the underlap loops of the facing warp yarns fed by another guide bar of the machine to be formed over the sinker members to a precisely controlled pile height. An example of this type of pile forming device is disclosed in Wunner U.S. Pat. No. 4,003,222. Through the use of their sinker members, these pile forming devices are capable of forming extended underlap loops on the technical fabric back to a pile height substantially greater than is achievable on the technical fabric face through the above-described overfeeding technique, because the facing yarns are fed and retained over the sinker members under controlled tension. Accordingly, the extended underlap pile produced utilizing these devices uniquely provides sufficient pile height for shearing to achieve a velour or velvet-like surface effect on the technical back of the fabric while providing the same generally smoothly surfaced technical face as the above-described conventional warp knitted fabrics.